The present invention relates to a method and apparatus for adjusting components of an optical system to correspond to positions of a user""s eyes and in particular to a system providing an optical signal to a user when adjustment is at least approximately correct.
Numerous optical devices are configured for outputting two different image paths, intended to be provided to a user""s left and right eyes. Examples of such devices include head mounted displays (HMDs), helmet mounted displays, binoculars, binocular microscopes and the like. In many such devices, it desirable to have the two (final) image optical paths substantially aligned with the user""s eye""s, e.g., such that the center (or other reference point) of each image falls substantially on the center of the user""s field of view. Departures from such a preferred alignment can have many undesirable consequences including loss of image quality, as perceived by the user, user eye strain or fatigue or, in extreme cases, potential for injury. Although some devices have included components intended to allow some amount of image position adjustment, previous approaches have generally been less than fully satisfactory.
In one approach, users are provided with an opportunity to provide a substantially symmetric adjustment of the lateral distance between the image paths. For example, some binoculars can be pivoted about a central hinge structure resulting in a change of the lateral distance between the two image paths. This approach, however, typically relies on a user""s ability to recognize, based on viewing the images themselves with the left and right eyes, when proper adjustment has been achieved. Many users find it difficult to recognize correct alignment based merely on viewing the images with their eyes and the consequent misalignment can lead to poor image quality, eye strain or eye fatigue, and general dissatisfaction of users. Accordingly, it would be useful to provide a system which can provide for at least some alignment of first and second images with left and right eyes without requiring users to judge or recognize the quality or degree of alignment based only on viewing the images.
Additionally, an arrangement such as that found in hinged binoculars can result in users being substantially unable to determine or verify when an alignment has been achieved which is sufficiently accurate to avoid the above-described problems. Accordingly, previous systems can provide an adjustment which achieves an alignment which the users might (incorrectly) subjectively judge to be good enough, but which may, in fact, be (perhaps only slightly) outside the range of adjustment needed to avoid the above-described problems. Accordingly, it would be useful to provide an adjustment system which more readily allows users to verify that alignment is within predefined minimum alignment accuracy ranges, preferably by providing a standard or indicator of alignment which does not rely on subjective judgment of the user.
Furthermore, a system such as the common hinged binocular system is a symmetric system, i.e., providing for left and right images which are equally distant from a center line or center of mass of the binoculars. Users often have at least small departures from bilateral symmetry in their eye locations (and/or center of left and right fields of vision) and systems which provide only symmetric adjustment, with respect to the structure of the optical device as a whole, can contribute to misalignment of images with respect to one or both eyes, particularly when the optical device is coupled to the user""s head, such as in a head-mounted display or a helmet-mounted display. Accordingly, it would be useful to provide a system which can, if desired, be implementing in a fashion permitting separate adjustment of left and right image positions and/or permitting asymmetric positioning of the images (with respect to, e.g., a center line or other fixed point on the optical device).
In addition to the common phenomenon of at least minor differences in the lateral position of user""s left and right eyes, it is not uncommon to find at least minor differences in the vertical position (e.g., with respect to the posterior-anterior axis) of user""s eyes. Misalignment of images in a vertical direction can also contribute to poor image quality, eye fatigue, eye strain and the like. Accordingly, it would be useful to provide an apparatus and method which can, if desired, be configured to allow the vertical position of the left and right images to be adjusted to respectively different vertical positions, preferably being adjustable separately (with respect to the optical device as a whole).
The present invention includes a recognition of the existence, nature and/or source of certain problems in previous approaches, including as described herein. In one aspect, the invention includes coupling a source of a relatively narrow-beam light to an image path device so that the narrow beam moves substantially with the image path as the image path is adjusted. Preferably, the device and method is configured so that users are provided with a substantially clearer indication of the alignment or relative alignment of the left and right images, with respect to the user""s eyes. For example, in one embodiment, the left and right lights will be invisible to a user until the image path has been adjusted to within a pre-determined tolerance of preferred alignment. In this embodiment, the user receives a substantially binary alignment indication, i.e., with the presence of a visible indicator light being indicative of alignment (within tolerance of a preferred alignment) and with the absence or invisibility of the light being indicative of incorrect or improper alignment. Preferably, the device can be configured such that, after alignment has been achieved, the indicator light or lights can be disabled so as to avoid interfering with further image viewing. In one embodiment, a device for forming a narrow and/or substantially non-dispersive light beam is coupled on, or with respect to, one or both of the optics that form or deliver an image to the left and right eyes along an image path, such that, as the image path is moved or adjusted, the location where the narrow beam will enter the user""s eye (if at all) will also change correspondingly. In one embodiment, a device for providing a narrow or non-dispersive beam includes a microlouvered film, receiving light from a light source, such as a light emitting diode (LED). In one embodiment, the adjustment for the lateral position of the image path of the left eye (with respect to the optical device as a whole) is independent from the adjustment for the lateral position of the image path for the right eye (with respect to the optical device as a whole), in the sense that adjusting the left image path lateral position has no effect on the right image path lateral position. In one embodiment, the apparatus and method allows adjustment, preferably independently, of the vertical position of the left and right image paths to achieve vertical alignment. Preferably, a narrow beam system is used for indicating vertical alignment to a user (which may be the same vertical beam used for indicating horizontal alignment or may be a separate narrow beam).
In one aspect, a head-mounted display or other optical device which provides at least a first image to at least one eye of a user can be adjusted for changing the alignment of an image path with respect to a user""s eye position. An alignment beam generator is mounted so as to move with the image path device so a user can use characteristics of the alignment beam to achieve a desired alignment of the image path. Preferably, the alignment beam is configured, such as by making it substantially narrow-beam, linear and/or non-dispersive, such that beam is substantially invisible to the user until it is within a preferred alignment range, so as to provide a binary or visible/invisible, indicator of alignment.